A contact adhesive utilizes initial tack to attach adherends. The initial tack occurs when the adhesive is applied to both surfaces of an adherend and the adhesive is left to stand for a predetermined period of time (after an open time). Contact adhesives have been long used in practice because they eliminate the need for temporary tacking or temporary holding, i.e., they are user friendly, and have an excellent balance of other physical properties. Contact adhesives, however, are solvent adhesives obtained by dissolving a polymer (e.g. natural rubber, synthetic rubber) in an organic solvent (to a solids concentration of 20 to 35%), and therefore have problems relating to labor environment, disaster prevention, and public hazard.
In order to solve these problems, aqueous emulsion adhesives have been considered, but they, currently, do not show satisfactory performance because they have problems such as low initial adhesion and a very long drying time particularly in winter.
Meanwhile, solventless contact adhesives containing a reactive silyl group-containing organic polymer (modified silicone polymer) which are considered to show performance equivalent to that of conventional solvent adhesives have been developed. Patent Literature 1, for example, discloses an adhesive including a modified silicone polymer and a (meth)acrylate copolymer with a reactive silyl group. This adhesive unfortunately takes a long time to develop its tack, showing performance which is not sufficiently satisfactory as an alternative for the current solvent contact adhesives. Patent Literatures 2 and 3 each disclose a contact adhesive containing a polymer with a trialkoxysilyl group, a polymer with a dialkoxysilyl group, and a (meth)acrylate copolymer. The trialkoxysilyl group is present at both terminals of the polymer in the adhesives described in these Patent Literatures. Such a polymer causes the adhesive to have too high a crosslink density during curing to reduce the initial stickiness, that is, the adhesive cannot achieve sufficiently high tack strength. The polymer with a trialkoxysilyl group at both terminals also causes immediate curing of only the surface of the adhesive after application (causes formation of a skin), which leads to a working life not long enough.